Various methods for treating or processing waste containing infectious material, i.e., waste containing various pathogenic microorganisms, are known in the art, and various technologies have been tested in attempts to effectively sterilize such wastes. However, the known, conventional processes have inherent disadvantages which limit their use.
The currently most widely used method of sterilizing or treating infectious wastes utilize thermal degradation as the primary treatment mechanism. The elevated temperatures used in these processes are generally achieved through dry air, steam or flame in order to sterilize infectious microorganisms by partial molecular degradation at lower temperatures or total molecular destruction at high temperatures.
An example of this type of method is the autoclave, which uses a combination of vacuum and pressurized steam to treat clinical products, such as instruments and containers, as well as to decontaminate post-patient care materials prior to disposal. The limitations of such sterilization systems include the possible escape of aerosolized and liquid borne pathogens through the drain and exhaust-ports of the system; the incomplete sterilization of materials containing pathogens resistant to the temperatures used; possible inadequate steam penetration to the center of the waste load; and the continuing requirement of storing, transporting and disposing the treated material, generally utilizing further incineration or landfills. Thus, this technology creates a secondary environmental problem relating to the disposal of the treated waste and is not designed to create any useful by-products from the treated materials.
Another conventional process utilizing thermal technology is incineration, which is presently the most commonly used infectious waste treatment method in the world. However, this technology is now coming under severe environmental criticism, and is subject to strict regulatory standards. In many instances, incineration is being banned entirely because of the likelihood that hazardous products are generated thereby. Thus, new guidelines regarding incineration involve higher standards relating to emissions, such as hydrogen chloride and carbon monoxide, and new requirements relating to dioxins and furans produced from burning complex plastic materials, such as polyesters. In order to comply with these standards, conventional incineration technology must be re-designed significantly, making these treatment methods economically unfeasible. The problems resulting from potential toxic emissions from incineration processes are an additional limitation to the traditional problems of intermediate storage and transport associated with this process, as well as the disposal of the residual ash in landfills.
A third conventional method of treating infectious waste which employs thermal technology comprises heating the waste in large scale microwave systems. Microwave systems are particularly effective for sterilizing water-based tissue and materials which allow the absorption of microwave frequencies. However, microwave systems have been found to be ineffective for achieving thermal sterilization of dry matter. Moreover, microwave methods do not penetrate materials shielded by metallic enclosures, such as needles, syringes, etc. Such processes are also expensive for large volume treatment and produce disinfected waste which requires further disposal, with its accompanying costs and problems.
Waste treatment processes employing the use of chemicals are also known and used in the art. In general, there are two major chemical methodologies utilized in waste treatment systems, utilizing both gas and liquid mechanisms. An example of a gaseous system comprises contacting the waste load with an appropriate amount of a gaseous chemical agent such as ethylene oxide, formaldehyde, peracetic acid and beta-propyl acetone in an appropriate treatment vessel, such as an atmospheric chamber. Ethylene oxide gas is widely used in the sterilization of thermolabile materials, which would otherwise be damaged by exposure to heat and moisture. However, these treatment processes have fallen into disfavor since the chemicals used are considered to be probable human carcinogens and require extreme care and containment during use. These materials also remain hazardous after treatment and require special detoxification procedures so that their concentration in the treatment area meets safety standards.
Waste treatment methodology employing liquid chemicals comprises the use of chlorine which is a very strong oxidizing agent and reacts in water to form hypochlorite ions. An example of a treatment methodology employing liquid chlorine comprises granulating the waste material and then subjecting the granulated particles to a chlorine spray or bath treatment. The chlorine treatment disinfects the granulated waste material by oxidizing the pathogens. However, such systems have limitations relating to the drying and final disposal of the chlorinated disinfected wastes, the safe disposal of the residual chlorinated treatment solution and the comprehensiveness of the exposure and subsequent inactivation of all pathogens embedded in the waste mass.
More recent, emerging infectious waste treatment processes employ advanced technologies originating from the fields of electronics and physics. Such processes achieve the destruction of infectious microorganisms within the waste by bombarding the waste load with electron beams or electromagnetic radiation. Examples of such methodology presently in use employ gamma radiation, electron beam radiation and ultraviolet radiation to destroy the pathogens present in the waste load.
For example, gamma irradiation systems utilize powerful radiation originating from radioactive sources such as Cobalt-60 and Cesium-137. Such systems are primarily used for the sterilization of medical supplies and food. However, recent high power gamma irradiation systems have been designed to treat large volumes of infectious waste materials in continuous conveyorized facilities. The disadvantages of such systems include the obvious hazards to personnel which require extra safety measures, such as shielding of the radiation units, which ultimately decreases the cost efficiency of these methods. Moreover, the effectiveness of such processes are dependent on the continual adjustment of exposure durations in order to accommodate for the continuous decay of the radioactive material. A more serious problem of these systems relates to the disposal of the spent radiation sources and the treated waste due to the existence of trace radioactivity therein.
Another treatment comprises subjecting the waste material to electron beam radiation utilizing electron energies exceeding 10.sup.7 electron volts. Commercial linear accelerators are used extensively for the small scale sterilization of surgical bandages and other disposable medical products. However, the use of electron beam energy for the sterilization and treatment of infectious waste material requires a large scale installation with attendant problems relating to costs and occupational safety procedures. For example, the possibility of workers absorbing low level secondary x-ray radiation remains and the disposal of the treated waste requires full secondary storage, transport and final disposition. Moreover, while this method is generally effective in destroying existent pathogens, the penetration efficiency of the electron beam energies diminishes with distance, density and the presence of metallic shielding in the waste material caused by needles, syringes, etc., thus limiting the guarantee of total disinfection of the treated material.
A third type of radiation technology now being used to treat infectious waste material utilizes ultraviolet radiation. However, it has been found that in general, ultraviolet wavelengths are effective only for the surface treatment of the waste materials and therefore, are not appropriate for the processing of infectious waste materials requiring subsurface penetration to accomplish sterilization. This characteristic limits the use of ultraviolet radiation for treating large volume mixed infectious waste.
Processes for eliminating or reducing the concentration of pathogens within waste materials to produce fertilizer materials are known in the art. For example, U.S. Pat. No. 3,953,191 discloses a process for ridding cotton gin waste of detrimental pathogens and weed seeds to produce a fertilizer. This process comprises chopping or grinding the gin waste and steaming the material by the temperature of 215.degree. F. and at constant pressure of 30 psig. U.S. Pat. No. 4,743,287 discloses a method of treating waste organic materials to produce a humic acid base fertilizer formulation which comprises granulating the material and then reacting the granulated material with water, acid and a base. A temperature of about 110.degree. to 280.degree. F. and a pressure of up to 30 psi is maintained in the reaction vessel. Also, U.S. Pat. No. 5,021,077 discloses a method of preparing natural nitrogenous particles useful as plant food by granulating waste material and then heating the material at a temperature of about 50.degree. to 100.degree. C. However, this patent discloses that heating at temperatures higher than 100.degree. C. disadvantageously causes the denaturing of proteins in the material. In contrast to the present method, none of these processes are directed to the treatment of infectious waste.
Accordingly, there is a need for a method for treating infectious waste material to substantially reduce or eliminate the concentration of pathogens therein, which is safe, effective, economical and which produces useful products.